Order statistics establishes a relation between the position of the ranked data and corresponding cumulative probability, so it can be used to estimate the cumulative probability. Owing to the fact that different climatological data have different skewness degrees, in this paper, according to the cumulative probability function under the skewed distribution conditions, we perform theoretical analysis and numerical simulation to establish the position parameters of the regression model which are related to skewness index, then give an amperic percentile formula under the skewed distribution. By using the data about the summer temperature in global from 1980 to 2009, we compare the positions of ranked data corresponding to the 90th percentile, which are obtained by this formula and Jenkinsons formula.